Rotary fuel pumps driven by an electrical powering device have been utilized for some years in vehicles either as original equipment or as appliances to supplement the original fuel supply system. The pump and power unit are frequently in a common housing as shown, for example, in U.S. Pat. No. 4,352,641, issued Oct. 5, 1982, to Charles H. Tuckey.
Since the pumps are frequently mounted in the fuel tanks of a vehicle, the noise factor is extremely important. A pump under load will normally produce more noise and this may be audible as a humming noise, to an annoying degree, to passengers in the vehicle. Various pulse dampening devices have been tried with some success but since they usually involve material such as a closed cell foam material or a hollow pulse dampening chamber of a synthetic flexible material, the useful life of these devices is limited by the vulnerability of the material in the presence of hydrocarbons.
Normally, during operation of these pumps, the media being pumped is in a liquid state and noise is at a minimum level. As the pumping cells are filled during the intake portion of the cycle, there are no voids, that is, no vapor in the pumping chamber when the exhaust ports are opened. If, however, a void or vapor is present (cavitation) in the pumping chamber when the exhaust port is opened, the pressure on the outlet side of the port can force fluid back through the exhaust port in a reverse direction into the pumping chamber to fill the void.
Since fuel in the outlet side of the exhaust port is normally at an operating pressure of, for example, 15 to 80 pounds per square inch, any reversal of flow through the exhaust port would be a very high velocity causing an impact noise. With a relatively standard rotation pump, this sequence can occur five times per revolution of the pumping rotor and at high speed can become very audible.
It is an object of the present invention to provide a pump construction which will avoid the reverse flow impact during cavitation and consequently materially reduce the noise of the pump operation under these circumstances.
It will be appreciated that in the pumping cycle as one pumping cell is exhausting, another cell is taking in fluid at the same time. In other words, intake and exhaust pressure waves are timed with one another, and normally the quantity of fluid being exhausted from each cell is the same as that being taken in by another cell.
The principle of the present invention lies in the elimination of the reversal of fluid flow through the exhaust port.
Another object of the invention is the interposition of a flexing device over the exhaust port adjacent the rotor to allow the escape of fluid under pressure but to prevent fluid under pressure from impacting back into the pumping chamber under cavitation conditions, namely, vapor conditions.
A further concept of the invention involves dividing the exhaust port area into several openings with a one-way valve at the discharge side of each port opening. This will allow liquid fuel under pressure to flow out and at the same time prevent any fluid pressure from backing up into the pumping chamber during a vapor or cavitation condition.
Other objects and features of the invention will be apparent in the following description and claims in which the principles of the invention are set forth together with details to enable a person skilled in the art to practice the invention, all in connection with the best mode presently contemplated for the invention.